1. Field of the Invention
The present invention relates to a jet-propulsion watercraft which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to a jet-propulsion watercraft, which can maintain steering capability even when the throttle is operated in the closed position and propulsion force is thereby reduced, and a cruising speed calculating device suitable for the watercraft.
2. Description of the Related Art
In recent years, so-called jet-propulsion personal watercraft (PWC) have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the personal watercraft, in association with a steering handle of a general bar type, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or left, to change the ejecting direction of the water to the right or to the left, thereby turning the watercraft.
A deflector is retractably provided behind the steering nozzle for blocking the water ejected from the steering nozzle. The deflector is moved downward to deflect the ejected water forward, and as the resulting reaction, the personal watercraft moves rearward. In some watercraft, in order to move rearward, a water flow is formed so as to flow from an opening provided laterally of the deflector along a transom board to reduce the water pressure in an area behind the watercraft.
In the above-described personal watercraft, when the throttle is moved to a substantially fully closed position and the water ejected from the water jet pump is thereby reduced, during forward movement and rearward movement, the propulsion force necessary for turning the watercraft is correspondingly reduced, and the steering capability of the watercraft is therefore reduced until the throttle is re-opened.
To solve the above-described condition with a mechanical structure, the applicant disclosed a jet-propulsion personal watercraft comprising a steering component for an auxiliary steering system which operates in association with the steering handle in addition to a steering nozzle for the main steering system in Japanese Patent Application No. Hei. 2000-6708.
The present invention addresses the above-described condition, and an object of the present invention is to provide a jet-propulsion watercraft, which can maintain steering capability according to the cruising speed thereof even when the operation which closes the throttle (hereinafter referred to as xe2x80x9cthrottle-close operationxe2x80x9d) is performed and the amount of water ejected from a water jet pump is thereby reduced, and a cruising speed calculating device suitable for the watercraft.
According to the present invention, there is provided a jet-propulsion watercraft comprising: a water jet pump that pressurizes and accelerates sucked water and ejects the water from an outlet port provided behind the water jet pump to propel the watercraft as a reaction of the ejecting water; an engine for driving the water jet pump; a steering operation means that operates in association with a steering nozzle of the water jet pump; a steering position sensor for detecting a predetermined steering position of the steering operation means; an engine speed sensor for detecting an engine speed of the engine; a cruising speed calculating means for calculating a cruising speed of the watercraft based on the engine speed detected by the engine speed sensor; and an electric control unit, wherein the electric control unit is adapted to increase the engine speed while a result detected by the steering position sensor is the predetermined steering position and a value calculated by the cruising speed calculating means is within a predetermined speed range.
According to the jet-propulsion watercraft, the engine speed is increased while the watercraft is steered, this operation is detected by the steering position sensor, and while the cruising speed calculated by the cruising speed calculating means based on the engine speed detected by the engine speed sensor is within a predetermined speed range. Therefore, the water sufficient to turn the watercraft is ejected from the water jet pump, and the steering capability can be maintained even when the throttle-close operation is performed.
Thus, a personal watercraft without a so-called cruising speed sensor can be placed in a steered state adapted to the actual cruising speed. In addition, since the cruising speed employed in the control process can be calculated from the engine speed, the personal watercraft is capable of obtaining the cruising speed without the normal cruising speed sensor, for example, the conventional hydraulic cruising speed sensor which tends to be clogged with contamination in water.
Herein, control for increasing the engine speed is referred to as xe2x80x9csteering assist mode controlxe2x80x9d, and the xe2x80x9cthrottle-close operationxe2x80x9d means that operation is performed to bring the throttle toward a closed position by a predetermined amount or more.
In the jet-propulsion watercraft, the cruising speed calculating means may include a speed conversion table that stores relationship between the engine speed and the cruising speed and is adapted to refer to the speed conversion table based on the detected engine speed to read out the cruising speed.
In the jet-propulsion watercraft, the cruising speed calculating means may further include: an offset table that stores an offset value used for offsetting the cruising speed stored in the speed conversion table according to a degree of acceleration/deceleration of the engine; and an obtaining means for obtaining the degree of acceleration/deceleration of the engine, and the cruising speed read from the speed conversion table can be offset according to the degree of acceleration/deceleration of the engine. Specifically, the cruising speed calculating means offsets the cruising speed by addition/subtraction based on the offset value read from the offset table and the cruising speed read from the speed conversion table. Thereby, a more accurate cruising speed in view of the inertia of the watercraft can be obtained.
In the jet-propulsion watercraft, the obtaining means for obtaining the degree of acceleration/deceleration of the engine may comprise: an engine speed memory for sequentially storing the engine speed detected by the engine speed sensor; a calculating means for calculating a difference value between two engine speeds stored in the engine speed memory; a difference value memory for sequentially storing the calculated difference value; and a cumulating means for cumulating the difference values stored in the difference value memory, and the degree of acceleration/deceleration of the engine can be calculated based on a cumulated value. The term xe2x80x9csequentiallyxe2x80x9d is herein defined as xe2x80x9cin time sequencexe2x80x9d. It should be noted that all of the engine speeds detected by the engine speed sensor in predetermined time cycles may be stored in the engine speed memory or they may be partially stored therein. Further, the engine speed sensor may detect the engine speed for every control clock or partially detect the engine speed.
The degree of acceleration/deceleration of the engine may be obtained indirectly by the calculation as described above, or otherwise may be obtained directly from a transducer provided on a crankshaft of the engine.
The jet-propulsion watercraft may further contain a throttle-close operation sensor for detecting throttle-close operation, and the engine speed can be increased while the steering operation is detected by the steering position sensor, the throttle-close operation is detected by the throttle-close operation sensor, and the value calculated by the cruising speed calculating means is within a predetermined speed range.
Also, the engine speed can be increased while the steering operation is detected by the steering position sensor, a decrease of a predetermined engine speed, i.e., the throttle-close operation is detected from the result detected by the engine speed sensor, and the value calculated by the cruising speed calculating means is within a predetermined speed range.
In this case, when the cruising speed becomes the predetermined speed after the throttle-close operation, transition to the steering assist mode control takes place. Therefore, the steering assist mode control can be effectively started according to the speed of the watercraft.
In the jet-propulsion watercraft, the throttle-close operation may be detected by a throttle position sensor.
It should be noted that the throttle-close operation sensor of the present invention is not limited to the engine speed sensor and the throttle position sensor. For example, it is possible to use a sensor placed in a system connecting a throttle lever and a throttle valve for detecting operation of the system when the throttle-close operation is performed. Also, it is possible to use a sensor for detecting an air-intake pressure and an air-intake amount of the engine.
Under the steering assist mode control, the engine speed can be increased by changing at least any of a fuel injection timing of a fuel injection system of the engine, an ignition timing of an ignition system of the engine, and a fuel injection amount of the fuel injection system of the engine. In this case, the engine speed can be increased without actual operation of the throttle.
It is preferable that the engine speed is increased up to approximately 2500 rpm-3500 rpm as an upper limit under the steering assist mode control.
It is preferable that the steering assist mode control is not executed particularly while the engine speed is within an idling range while the watercraft is moving forward because this is unnecessary. The idling range is defined as the range from the idling speed to a speed slightly higher than the idling speed and is preferably below approximately 2500 rpm.
The steering assist mode control may be executed even while the watercraft is moving rearward. In this case, it is preferable that the control is executed even while the engine speed is within the idling range.
According to the present invention, there is also provided a cruising speed calculating device used for a jet-propulsion watercraft provided with a water jet pump that pressurizes and accelerates sucked water and ejects the water from an outlet port provided behind the water jet pump to propel the watercraft as a reaction of the ejecting water, comprising: an engine speed sensor for detecting an engine speed of an engine for driving the water jet pump; and a cruising speed calculating means for calculating a cruising speed based on the engine speed detected by the engine speed sensor, wherein the cruising speed calculating means includes a speed conversion table that stores relationship between the engine speed and the cruising speed and is adapted to refer to the speed conversion table based on the detected engine speed to read out the cruising speed.
The cruising speed calculating device of the present invention provides a cruising speed detecting means suitable for the personal watercraft which does not comprise the conventional hydraulic cruising speed sensor subjected to contamination in water.
In the cruising speed calculating device, the cruising speed calculating means may comprise: an offset table that stores an offset value used for offsetting the cruising speed stored in the speed conversion table according to a degree of acceleration/deceleration of the engine; and an obtaining means for obtaining the degree of acceleration/deceleration of the engine, and the cruising speed read from the speed conversion table may be offset based on the offset value read from the offset table. Specifically, the cruising speed calculating means performs offset by addition/subtraction of the cruising speed read from the speed conversion table. Thereby, a more accurate cruising speed in view of the inertia of the watercraft can be obtained.
In the cruising speed calculating device, the obtaining means may include an engine speed memory for sequentially storing the engine speed detected by the engine speed sensor; a calculating means for calculating a difference value between two engine speeds stored in the engine speed memory; a difference value memory for sequentially storing the calculated difference value; and a cumulating means for cumulating the difference values stored in the different value memory, and the degree of acceleration/deceleration of the engine can be calculated based on a cumulated value. It should be noted that all of the engine speeds detected by the engine speed sensor in predetermined time cycles may be stored in the engine speed memory or they may be partially stored therein. Further, the engine speed sensor may detect the engine speed for every control clock or partially detect the engine speeds.
The degree of acceleration/deceleration of the engine may be obtained indirectly by the calculation as described above, or otherwise may be obtained directly from a transducer provided on a crankshaft of the engine.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.